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1, the so-called peristomial polykinety , and the proter\u2019s paroral or haplokinety . A new germinal kinety prolifer- ates from the paroral of both filial cells prior to completion of stomatogenesis. This pattern has been confirmed for Astylozoon (Guinea, Sola, Rueda, & Fernández-Galiano, 1988), Carchesium (Esteban & Fernández-Galiano, 1989), Opercularia (Fernández-Galiano, Esteban, & Munoz, 1988), Opisthonecta (Sola, Guinea, & Fernández-Galiano, 1985), and Thuricola (Eperon, 1980). Foissner (1996b) characterizes this as an ophryobuccokinetal stomatogenesis since the opisthe\u2019s oral apparatus derives from an ophryo \u2212 or germinal kinety , sug- gesting homologies to the process in peniculines , but also to that of the scuticociliates . Indeed, it is to the latter group, and particularly the thigmotrichs , to which the common ancestry of the peritrichs has been linked (Fauré-Fremiet, 1950a; Lom, 1964). We currently need some gene sequences from thigmotrichs to explicitly test this hypothesis. However, the gene sequence database currently does not support it: peritrichs are consistently a strongly supported sister clade to the hymenos- tomes and not to the scuticociliates (Affa\u2019a et al., 2004; Miao et al., 2004b). The last two groups of oligohymenophore- ans , the apostomes and astomes , are problematic because they are so divergent. Astomes , of course, have no stomatogenesis, since by definition they have no mouth. They divide transversely, equally or unequally (Fig. 15.5). In the latter case, they may remain attached as chains of cells or catenoid \u201ccol- onies\u201d (Beers, 1938; de Puytorac, 1954, 1994g). Subsequent cell growth and division may involve only the anterior cell (e.g., Hoplitophrya ) or each filial cell may grow and divide (e.g., Cepedietta ) but not separate (de Puytorac, 1994g). Apostome division morphogenesis demonstrates no clear homologies with other oligohymenopho- reans , presumably a result of the highly unusual life cycle of these ciliates. \u201cStomatogenesis\u201d and morphogenesis during the life cycle have been studied in Hyalophysa using protargol staining (Fig. 15.11) (Bradbury, Song, & Zhang, 1997; Landers, 1986). The anterior kinety, kinety a , plays a central role in the replication of cortical structures. It elongates by replication of a small, anterior fragment in the trophont , and apparently differentiates into three bipolar kineties, named a , b , and c . The latter kinety dedifferentiates com- pletely, b may differentiate as the paroral , and a provides continuity as the kinety a for the next round of fission (Bradbury et al., 1997). Bradbury et al. (1997) noted that kinety a in Foettingeria derives from Kinety 1. Thus, this is a kind of monoparakinetal stomatogenesis , like that of Tetrahymena , since kinety a provides an oral structure, the paroral homologue . This is also consistent with preliminary gene sequence data that place apostomes within the oligohy- menophorean clade, although not close to the hymenostomes (J.C. Clamp et al., 2008; Lynn et al., 2005). A discussion of division morphogenesis of oli- gohymenophoreans would not be complete without some reference to the extensive literature on the cell and developmental biology of the process, most recently reviewed by Frankel (1989, 1991). Simply, the process can be viewed as a duplication 15.5 Division and Morphogenesis 319 320 15. Subphylum 2. INTRAMACRONUCLEATA: Class 9. OLIGOHYMENOPHOREA of structure controlled at two major levels \u2013 at the level of the organelles and organellar complexes and at the level of the cell as a whole. At the organellar complex level , the working hypoth- esis has long been that the local environment and pre-existing structure play determining roles, so-called structural guidance or cytotaxis (Frankel, 1989; Sonneborn, 1964; Williams, 1986). There is now convincing evidence for this in the propaga- tion, over many cell cycles, of a patch of inverted somatic kineties (Beisson & Sonneborn, 1965; Ng & Williams, 1977). Furthermore, successful repli- cation is dependent upon the presence of specific, kinetosome-associated structures (Iftode & Fleury- Aubusson, 2003; Kaczanowska et al., 1996). The inversion of these kinetids also causes the beat cycle of their cilia to be opposite to those of adjacent, normally-oriented kinetids (Tamm, Sonneborn, & Dippell, 1975). For the Paramecium cell as a whole, there is suggestive evidence that morphogenetic waves , originating from the oral apparatus and fis- sion furrow, induce duplication and reorganization processes (Iftode et al., 1989). Migration of the new oral structures, essential to the completion of normal division in all oligohymenophoreans but hymenostomes , depends upon proper disassembly and reassembly of cortical structures (Kaczanowska et al., 1995). When the oral development in the two cells is almost complete, cytokinesis occurs, accom- panied by the appearance of a contractile ring of microfilaments at the fission furrow (Eperon, 1985; Jerka-Dziadosz, 1981c; Yasuda, Numata, Ohnishi, & Watanabe, 1980). Assembly of a functional contractile ring depends upon Ca 2+ and several proteins, including calmodulin and actin (Gonda & Numata, 2002; Williams et al., 2006). Oligohymenophoreans have limited powers of regeneration. Nevertheless, as in other classes, regeneration after microsurgery has been demon- strated in some peniculines (Chen-Shan, 1979) and hymenostomes (Mugard & Lorsignol, 1956). 15.6 Nuclei, Sexuality and Life Cycle The oligohymenophoreans present a broad diver- sity of forms in the macronucleus . Typically, the macronucleus is single and globular to ellipsoid (Figs. 15.2\u201315.5). Variations do exist: peritrichs are typified by the horseshoe- or band-shaped macronucleus (Fig. 15.3) (Lom, 1994); astomes may have a macronucleus extending along the entire length of the body, sometimes with irregu- lar extensions (Fig. 15.5) (de Putyorac, 1994g); a rare scuticociliate can have multiple fragments of the macronucleus (Lynn & Frombach, 1987); and apostomes demonstrate a variety of macronuclear forms with one form showing a complex network (Fig. 15.2) (de Puytorac, 1994h). The micronucleus is typically solitary, although some species are typified by having two micronu- clei. In rare exceptions, over 40 micronuclei have been observed in particularly large-bodied forms (Lynch, 1929; Lynn & Berger, 1973). The micro- nucleus of oligohymenophoreans can have from five chromosomes in Tetrahymena (Ray, 1956) to several hundreds in Paramecium species, and some Paramecium species may be polyploid (Aury et al., 2006; Raikov, 1982). Micronuclear morphol- ogy can vary both between and within genera. For example, four different types of micronuclei have been identified by Fokin (1997) among ten different Paramecium species: these are vesicular, endosomal, chromosomal, and compact types. Macronuclear ploidy varies typically with the sizes of the cell and the macronucleus: the larger mac- rostome species of Tetrahymena may be 450 × n; larger Paramecium species over 850 × n; and the large trophonts of Ichthyophthirius set an oligohy- menophorean record of 6,300 × n (Raikov). Both kinds of nuclei in oligohymenophoreans divide with the aid of microtubules. Intramacro- nuclear microtubules have been observed in dividing Paramecium and Tetrahymena (Nilsson, 1976; Tucker, Beisson, Roche, & Cohen, 1980) and myosin has been implicated by immunofluorescence studies (Hauser, Beinbrech, Gröschel-Stewart, & Jockusch, 1975). Analysis of mutant phenotypes of Paramecium and drug and heat treatments of Tetrahymena provided support for the model that microtubular sliding elongates the macronucleus (Cohen, Beisson, & Tucker, 1980; Nilsson, 1976). Nevertheless,